Oxidizing catalytic converters may be present in the exhaust stream of motor vehicles in order to reduce the emission of pollutants produced during combustion. For example, unburnt fuel and carbon monoxide (CO) may be converted to less toxic substances, such as carbon dioxide and water, before being released to the atmosphere.
However, high exhaust temperatures and the heat released during oxidation can cause aging and degradation of an oxidizing catalytic converter resulting in increased emissions. Various methods may be employed to monitor the aging and consequent degradation in performance of an oxidizing catalytic converter. In one method, the concentration of unburnt hydrocarbons in the exhaust may be increased via post-injection or direct injection of fuel into the exhaust and a temperature rise within the oxidizing catalytic converter may be observed.
The inventors herein have identified potential issues with the above approach. The temperature increase within the oxidizing catalytic converter caused by oxidizing a higher concentration of unburnt hydrocarbons is minimal: about 10 to 20° C. Therefore, the reliability with which a distinction can be made between a robust (less aged) and a degraded (greatly aged) oxidizing catalytic converter is lower. Further, the oxidizing catalytic converter may store hydrocarbons which may be oxidized only after the catalytic converter has reached light-off temperatures thus, inadvertently contributing to the increase in catalyst temperature and resulting in erroneous readings.
The inventors herein have recognized the above issues and identified an approach to at least partly address the issues. In one example approach, a method for monitoring the aging of an oxidizing catalytic converter in the exhaust stream of an engine is provided. The method comprises monitoring oxidation action of the converter after artificially generating an increase in feedgas carbon monoxide levels. A degree of aging of the catalytic converter is determined based on the oxidizing action of the converter.
In one example, when the oxidizing catalytic converter is above its light-off temperature, carbon monoxide levels in the exhaust stream may be artificially increased for short durations, for e.g., by operating the engine under a lean mode, and oxidation action may be monitored. Herein, oxidation action may be measured based on the oxidation efficiency of carbon monoxide. An aged oxidizing catalytic converter may be indicated when carbon monoxide oxidation efficiency is reduced and a fraction of carbon monoxide in the gases exiting the oxidizing catalytic converter are higher than an allowable threshold.
In another example, oxidation action may be evaluated during temporarily increased carbon monoxide conditions by monitoring the temperature rise within the oxidizing catalytic converter during the oxidation process. An aged oxidizing catalytic converter may be indicated when the rate of temperature increase within the oxidizing catalytic converter is slower than an expected rate.
In this way, aging can be assessed by artificially increasing feedgas carbon monoxide levels to enable more reliable data regarding oxidizing action of the catalytic converter. By focusing on the oxidation of carbon monoxide, instead of unburnt hydrocarbons, more accurate results may be obtained because the oxidation of carbon monoxide causes a significant temperature increase in the oxidizing catalytic converter. Additionally, carbon monoxide, unlike unburnt hydrocarbons, is not stored within the oxidizing catalytic converter prior to light-off temperature. Thus, an observed temperature rise within the oxidizing catalytic converter may be correlated with the oxidation of carbon monoxide flowing through the catalyst. By increasing carbon monoxide levels after light-off, emissions can be kept within acceptable limits. By operating the engine in a lean mode, the content of unburnt hydrocarbons in the exhaust gas stream can be held at lower concentrations while providing sufficient carbon monoxide for catalytic converter diagnosis.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.